Enter the lumens exiting the lamp and the total lumens reaching the desired plane into the calculator to determine the coefficient of utilization.

Coefficient of Utilization Formula

The following equation is used to calculate the Coefficient of Utilization.

CU = LRP / LU

  • Where CU is the coefficient of utilization
  • LRP is the luminous flux reaching the desired plane (lumens)
  • LU is the total luminous flux emitted by the fixture (lumens)

To calculate the coefficient of utilization, divide the luminous flux reaching the desired plane by the luminous flux emitted by the fixture.

What is a Coefficient of Utilization?

Definition:

A coefficient of utilization is a measure of the ratio or percentage of luminous flux that reaches the desired plane when emitted from a lighting fixture.

How to Calculate Coefficient of Utilization?

Example Problem:

The following example outlines the steps and information needed to calculate the Coefficient of Utilization.

First, determine the total luminous flux emitted by the fixture. In this example, the flux is 5000 lumens.

Next, determine the luminous flux that reaches the desired plane. In this case, this value is 2000 lumens.

Finally, calculate the coefficient of utilization using the formula above:

CU = LRP / LU

CU = 2000 / 5000

CU = .4